The present invention relates generally to medium access control in communication networks.
Wireless data networks are used in many different applications as a cost-effective solution for transporting data from one point to another. Such networks are typically characterized by many individual users located at nodes distributed over a geographic area. Such networks typically use an access point (AP) based architecture in which APs aggregate wireless data from users within a certain geographic region and then transport this aggregated data traffic over a backhaul network from the APs to a core network, such as a service provider's network. In many cases, the service provider's network is the Internet. In some implementations, data from a user must make multiple wireless hops between access points and other network nodes before reaching the core network. With the increasing adoption of high-speed wireless access technologies such as the well known 3G and IEEE 802.11a/g wireless technologies, such multi-hop wireless backhaul networks are emerging as a cost-effective solution to meet the requirements of broadband wireless access. Compared with wired networks, wireless backhaul networks not only significantly reduce network deployment cost, but also enable fast and flexible network configuration. Furthermore, a multi-hop wireless architecture, also referred to herein as a mesh network, can extend network coverage and provide increased reliability due to the existence of multiple routes between source and destination nodes. Such an alternative routing potential ensures high network availability when node or link failures occur or when channel conditions are poor.
For multi-hop wireless networks, a significant factor limiting network capacity is the interference between neighboring network links and nodes. One technique for overcoming these limitations uses multiple cooperating antennas to increase the throughput and/or substantially reduce the transmit power of the communication system. Such techniques may be implemented, illustratively, using well-known Multiple Input, Multiple Output (MIMO) algorithms at the physical layer (PHY) of a backhaul network to exploit phenomena such as multipath propagation to increase throughput, or reduce bit error rates, rather than attempting to eliminate effects of multipath propagation distortion. Such techniques are useful to reduce the impact of interference on neighboring nodes as well as to reduce the required transmit power for a signal.
Due to the high volume of wireless data traffic in such networks, wireless radio resource allocation becomes increasingly complex. Specifically, in many cases neighboring links cannot be actively transmitting simultaneously due to the aforementioned interference between neighboring transmissions (also referred to herein as secondary conflicts) as well as the half-duplex characteristic of the wireless transceiver (also referred to herein as primary conflicts). Thus, scheduling at the Medium Access Control (MAC) layer in the network becomes increasingly difficult as the number of neighboring links increases. Additionally, since the transmission of data across different wireless links are highly interdependent in multi-hop mesh networks, routing and scheduling are also interrelated. Finally, MAC layer scheduling directly depends on the interference levels which are determined by the physical layer operations. Thus, in today's complex wireless multihop networks, MAC layer scheduling, PHY layer beamforming and network layer routing are interdependent. Prior attempts, however, have typically treated these functions as being independent problems, leading to suboptimal network performance.